CN113891754A

CN113891754A - Method for processing waste plastic pyrolysis gas

Info

Publication number: CN113891754A
Application number: CN202080040051.0A
Authority: CN
Inventors: 安蒂·库尔基耶尔维; 汉努·莱赫蒂宁; 埃萨·科尔霍宁; 米科·马蒂莱宁; 马克斯·奈斯特伦
Original assignee: Neste Oyj
Current assignee: Neste Oyj
Priority date: 2019-06-10
Filing date: 2020-06-01
Publication date: 2022-01-04
Also published as: US11471817B2; CA3134582A1; EP3946667A1; EP3946684A1; SG11202111642XA; CA3134361A1; FI128804B; CN113891757A; US11969689B2; WO2020249854A1; FI3946667T3; CA3134582C; US20220226765A1; EP3946684A4; US20230042698A1; SG11202111641UA; EP3946667A4; WO2020249853A1; CA3134361C; EP3946667B1

Abstract

The present invention relates to a process for processing waste plastic pyrolysis gas, in particular wherein clogging of the system used in the process is avoided or at least mitigated.

Description

Method for processing waste plastic pyrolysis gas

Technical Field

The present invention relates to a process for processing waste plastic pyrolysis gas, in particular wherein clogging of the system used in the process is avoided.

Background

A large amount of waste plastics is produced worldwide. For example, municipal solid waste plastic typically includes High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), polypropylene (PP), Polystyrene (PS), poly (vinyl chloride) (PVC), and poly (ethylene terephthalate) (PET). This is a rich feedstock that can be used as an alternative refinery feed as well as a platform for new plastics and chemicals. However, solid plastics are not suitable raw materials per se, which first of all need to be liquefied. The yield and composition of the product are influenced primarily by the type of plastic and the operating conditions (Williams et al energy & Fuels,1999,13, 188-.

The processing of waste plastics is carried out in chemical recycling systems and it relies on thermal pyrolysis reactions to crack long chain plastic polymers into shorter products, most of them being liquids. Gaseous product mixtures from the pyrolysis of plastics are known to plug and contaminate surfaces, pipes and equipment. This is partly because some of the reaction products are heavy waxy components that deposit on the surface, but tars, char, and more solid coke type deposits are common. Waxy components and tars are particularly problematic on the cooling surfaces of the heat exchangers used in the condensation of the reaction mixture, but coke can be deposited anywhere in the equipment. These cause two major problems. First, the deposits act as an insulating material that reduces heat transfer in the heat exchanger. Secondly, the deposits will eventually clog the heat exchanger, thereby preventing any fluid from passing therethrough. Therefore, if a conventional heat exchanger is used to condense the pyrolysis gas, the equipment needs to be multiplied: while one device is operating, the other is in service and clean. This is expensive and labor intensive.

This problem has been addressed prior to the use of direct contact condensers. However, for example, spray condensers suffer from relatively low separation efficiency, and they do not provide protection against coke deposition. In addition, the liquid recirculation used in these condensers requires a liquid hold-up which has two major drawbacks. First, it significantly increases the combustion load (fire load) of the plant due to the presence of a hot pyrolysis product mixture storage tank in the recycle loop. Second, the relatively long residence time (tolerance time) of the liquid storage tank exposes the liquid to additional thermal reactions, potentially degrading product quality and causing equipment contamination.

EP3031881a1 discloses a process for processing waste plastic pyrolysis gas. The method comprises pre-purification of the waste pyrolysis gas by passing it through a collection chamber for removal of carbides and then through a cyclone for removal of larger solid impurity particles. Then, the prepurified waste plastic pyrolysis gas is purified from the remaining particles and the heavy oil fraction by spraying the prepurified gas at a temperature of about 400 ℃ and 500 ℃ with oil at a temperature of about 70-110 ℃. For example, spraying is carried out by using a Venturi scrubber.

US2003047437a1 discloses a process for the pyrolysis of waste plastic to produce a hydrocarbon finish. The process comprises pyrolyzing waste plastic to form a hydrocarbon finish, gravity separating the gaseous pyrolysis products, quenching the separated gaseous pyrolysis products by primary cooling of the liquid pyrolysis products and delivering the resulting mixture to a fractionation column for subsequent cooling and fractionation of the gaseous and liquid fractions.

JPS4952172A discloses a method for treating polymer waste, such as PVC pyrolysis gas. The process comprises feeding a synthetic polymer to a furnace and spraying waste oil into a scrubber tower whereby the oil is heat exchanged with gaseous products from the furnace that are separated into volatile and liquid components. The gaseous product from the liquid-gas separation column is directed to another separation column and recovered as gas and liquid hydrocarbons.

CN109603376A discloses a system for processing waste plastic pyrolysis gas.

Therefore, there is still a need for further processes for processing waste plastic pyrolysis gas in which the risk of clogging of the systems used in the process is reduced.

Disclosure of Invention

The following presents a simplified summary in order to provide a basic understanding of some aspects of various embodiments of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to the more detailed description of example embodiments of the invention.

It was observed that when the gaseous reaction mixture from the pyrolysis of waste plastics was mixed with the cooled, condensed pyrolysis product, the highest boiling fraction of the pyrolysis gas was smoothly condensed from the mixture without clogging.

It was also observed that clogging of waste plastic pyrolysis products can be avoided by passing the gaseous pyrolysis products through a condensing unit operating at a temperature below the pyrolysis temperature when wiping and/or scraping any solidified material from the inner walls of the condensing unit.

According to the present invention, there is provided a novel process for processing waste plastic pyrolysis gas, the process comprising

a) Provide for

Omicron waste plastic pyrolysis gas stream, wherein the temperature of said waste plastic pyrolysis gas stream is 300-650 ℃, preferably 450-500 ℃, and

a hydrocarbon liquid stream, wherein the temperature of the hydrocarbon liquid stream is lower than the temperature of the waste plastic pyrolysis gas stream,

b) mixing the plastic pyrolysis gas stream and the hydrocarbon liquid stream in a spraying device to form a mixture,

c) spraying the mixture into a chamber through a spray nozzle to produce a condensed fraction and a gaseous fraction, an

d) Separating the gaseous fraction and the condensed fraction to obtain a first liquid product stream and a gaseous product stream.

Some exemplary and non-limiting embodiments of the invention are described in the appended dependent claims.

The various illustrative and non-limiting embodiments and methods of operation of this invention, as well as other objects and advantages thereof, will be best understood from the following description of specific exemplary embodiments when read in connection with the accompanying drawings.

The verbs "comprise" and "comprise" are used in this document as open-ended limitations that neither exclude nor require the presence of unrecited features. The features recited in the dependent claims are freely combinable with each other, unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" (i.e., singular forms) throughout the document does not exclude a plurality.

Drawings

The exemplary and non-limiting embodiments of the invention and their advantages are explained in more detail below with reference to the accompanying drawings, in which

FIG. 1 shows an exemplary non-limiting system suitable for processing waste plastic pyrolysis gas in accordance with an embodiment of the invention.

Detailed Description

The present invention relates to the processing of waste plastic pyrolysis gas to avoid or at least mitigate fouling of the systems used in the process.

Fig. 1 shows an exemplary system 100 suitable for use in a method according to an embodiment of the invention. According to this embodiment, the method comprises co-introducing a waste plastic pyrolysis gas stream (a) and a hydrocarbon liquid stream (B) to the injection device 101 to form a mixture (C). The temperature of the waste plastic pyrolysis gas stream is typically 300-650 ℃, preferably 450-500 ℃. The temperature of the hydrocarbon liquid stream is lower than that of the waste plastic pyrolysis gas stream, typically 100-. An exemplary temperature of the hydrocarbon liquid stream is 200 ℃. Proper mixing will ensure adequate contact between the two phases and cooling of the sparge gas so that the highest boiling portion of the sparge gas condenses.

After mixing, the mixture is preferably directed through spray nozzle 102 to chamber 103 where the liquid and gas separate and form a condensed liquid fraction (D1) and a gas fraction (E1). The chamber comprises outlets for gas and liquid.

Thus, good contact between the liquid and gas phases is achieved because the gaseous pyrolysis reaction mixture is thoroughly mixed with the cooled hydrocarbon liquid before it enters the chamber. This result leads to improved, more desirable condensation behavior and more desirable separation. In addition, because the mixing is carried out by means of nozzles in the injection device, the flow rate is sufficiently high that the injection device is not contaminated, while still having the same advantages as other direct contact condensers. An exemplary device comprising a spray device, nozzle and chamber is a spray Venturi scrubber.

The mass ratio of liquid to gas in the mixture should be high enough to avoid excessive cooling. The mass ratio is usually 1 to 100, preferably 5 to 25. An exemplary mass ratio is 12.

When the mixture is injected through the nozzle into the chamber, liquid and gas phases are formed and the liquid fraction and the gas fraction are separated to obtain a first liquid product stream (D1) and a gas product stream (E1).

According to a preferred embodiment, a first portion (D1a) of the first liquid product stream is recycled, e.g., pumped from chamber 103 back to injection device 101 through line 104, and a second portion (D1b) of the first liquid product stream is collected from the process as "heavy product" to collection device 105. The yield and composition of the heavy products depend mainly on the nature of the waste plastic, the pyrolysis conditions and the condensation temperature.

To avoid plugging, line 104 and thus the first portion of the first liquid product stream therein is preferably maintained at a temperature above 100 ℃, more preferably at 150 ℃ to 250 ℃. The desired temperature range may be obtained by insulating the pipeline and/or using one or more heating devices. An exemplary temperature of the first portion of the first liquid product stream is 200 ℃.

According to a preferred embodiment, the gaseous fraction, i.e. the gaseous product stream (E1), is conducted from chamber 103 via line 106 to condensing means 107. The condensing means is typically a conventional heat exchanger. According to an exemplary embodiment, the temperature of the gas product stream is reduced in the condensation device 107 to 10-50 ℃, preferably 20-40 ℃. Cooling produces a condensate and a non-condensable gas. Since most of the heavies have been removed, no contamination or plugging is expected in line 106 and in condensing unit 107. The condensed liquid (D2) is separated from the non-condensable gases (E2) to obtain a second liquid product stream, i.e. light products. It may be transferred to a collection device, such as a storage tank 108. The yield and composition of the light products depend on the nature of the waste plastic, the pyrolysis conditions and the condensation temperature. The non-condensable gases may be directed for combustion or to one or more other collection devices.

According to the embodiment shown in fig. 1, the process comprises co-introducing a waste plastic pyrolysis gas stream and a hydrocarbon liquid stream to an injection device. To initiate the process, the system is filled with seed crystal liquid (seed liquid). The seed crystals are typically condensed waste plastic pyrolysis gases from previous processes. Alternatively, another hydrocarbon liquid composition having similar properties may be used. The aim was to verify that at the start of the process, in the injection device, the system included sufficient hydrocarbon liquid material mixed with the waste plastic pyrolysis gas stream.

Experiment of

The process was simulated using Aspen plus software. Pyrolysis gas was modeled using pseudo components (pseudo components) estimated using distillation curves and densities from experimental measurements of crude plastic pyrolysis oil. The density used was 809.8kg/m³And table 1 provides the True Boiling Point (TBP) distillation curve.

TABLE 1

Recovery quality (%)	Temperature (. degree.C.)
		2	36.0
5	68.6
		10	97.4
30	171.9
		50	236.0
70	316.0
		90	430.4
95	474.3
		100	582.4

In addition, the amount and composition of the light fraction were estimated from literature (Williams et al, Energy & Fuels,1999,13, 188-. The mass ratio of the light fraction and the pseudo fraction was 0.27, and the composition of the light fraction is provided in table 2.

TABLE 2

Light products	wt-％
		Methane	36.3
Ethylene	2.2
		Ethane (III)	28.9
Propylene (PA)	4.7
		Propane	19.9
Butene (butylene)	1.5
		Butane	6.7

The thermodynamic model used in the simulation was Braun K-10 and it assumed that there was an ideal separation stage in the injection device.

A pyrolysis gas stream of waste plastics having a pressure (a) of 95kPa, a temperature of 500 ℃, an average molar weight of 69.2g/mol and a mass flow of 20kg/h leaves the reactor.

The pygas is passed to a Venturi ejector where it is contacted with a stream of recycled hydrocarbon liquid. The mass ratio of the hydrocarbon liquid to the waste plastic pyrolysis gas was about 100. A Venturi eductor sprays the mixture into the separation chamber and pumps the condensed heavy hydrocarbons through a shell and tube heat exchanger. The heat exchanger is adjusted so that the temperature of the resulting mixture is from 100 to 300 ℃. After the heat exchanger, the liquid heavy hydrocarbons are separated and partially recycled back to the Venturi ejector and partially tapped off and collected.

The non-condensable gases leave the separator tank through a demister (demister) and are led to a heat exchanger. The process side of the heat exchanger had an output temperature of 40 ℃. The condensed light hydrocarbons and non-condensables are fed to a knock-out drum, from which the non-condensables are fanned out and directed to incineration, and the liquid is collected. Tables 3-5 provide results from 3 simulation scenarios.

TABLE 3

TABLE 4

TABLE 5

The specific examples provided in the description provided above should not be taken as limiting the scope and/or applicability of the appended claims.

Claims

1. A process for processing waste plastic pyrolysis gas, the process comprising:

a) provide for

b) mixing the waste plastic pyrolysis gas stream and the hydrocarbon liquid stream in an injection device (101) to form a mixture,

c) spraying the mixture into a chamber (103) through a spray nozzle (102) to produce a condensed fraction and a gaseous fraction, an

2. The process according to claim 1, wherein the temperature of the hydrocarbon liquid stream of step a) is 100-.

3. A process according to claim 1 or 2, wherein the mass ratio of the hydrocarbon liquid stream and the waste plastic pyrolysis gas stream in the mixture is from 1 to 100, preferably from 5 to 25.

4. The method of any one of claims 1 to 3, further comprising recycling a first portion of the first liquid product stream to the hydrocarbon liquid stream of step a), and collecting a second portion of the first liquid product stream.

5. The process according to claim 4, wherein the temperature of the first part of the first liquid product stream is above 100 ℃, preferably from 150 ℃ to 250 ℃.

6. The process of any one of claims 1 to 5, wherein the hydrocarbon liquid stream of step a) comprises a first portion of a first liquid product stream.

7. The process according to any one of claims 1 to 6, comprising cooling the gaseous product stream of step d) to 10-50 ℃, preferably 20-40 ℃, thereby obtaining a second liquid product stream and a gaseous stream.

8. The method of claim 7, comprising separating the second liquid product stream and the gas stream.